/* Copyright Joyent, Inc. and other Node contributors. All rights reserved.
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to
 * deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#include "uv.h"
#include "tree.h"
#include "internal.h"

#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <errno.h>

#include <sys/types.h>
#include <unistd.h>

struct watcher_list {
    RB_ENTRY(watcher_list)
    entry;
    QUEUE watchers;
    int iterating;
    char* path;
    int wd;
};

struct watcher_root {
    struct watcher_list* rbh_root;
};
#define CAST(p) ((struct watcher_root*)(p))

static int compare_watchers(const struct watcher_list* a,
    const struct watcher_list* b)
{
    if (a->wd < b->wd)
        return -1;
    if (a->wd > b->wd)
        return 1;
    return 0;
}

RB_GENERATE_STATIC(watcher_root, watcher_list, entry, compare_watchers)

static void uv__inotify_read(uv_loop_t* loop,
    uv__io_t* w,
    unsigned int revents);

static int new_inotify_fd(void)
{
    int err;
    int fd;

    fd = uv__inotify_init1(UV__IN_NONBLOCK | UV__IN_CLOEXEC);
    if (fd != -1)
        return fd;

    if (errno != ENOSYS)
        return -errno;

    fd = uv__inotify_init();
    if (fd == -1)
        return -errno;

    err = uv__cloexec(fd, 1);
    if (err == 0)
        err = uv__nonblock(fd, 1);

    if (err) {
        uv__close(fd);
        return err;
    }

    return fd;
}

static int init_inotify(uv_loop_t* loop)
{
    int err;

    if (loop->inotify_fd != -1)
        return 0;

    err = new_inotify_fd();
    if (err < 0)
        return err;

    loop->inotify_fd = err;
    uv__io_init(&loop->inotify_read_watcher, uv__inotify_read, loop->inotify_fd);
    uv__io_start(loop, &loop->inotify_read_watcher, POLLIN);

    return 0;
}

static struct watcher_list* find_watcher(uv_loop_t* loop, int wd)
{
    struct watcher_list w;
    w.wd = wd;
    return RB_FIND(watcher_root, CAST(&loop->inotify_watchers), &w);
}

static void maybe_free_watcher_list(struct watcher_list* w, uv_loop_t* loop)
{
    /* if the watcher_list->watchers is being iterated over, we can't free it. */
    if ((!w->iterating) && QUEUE_EMPTY(&w->watchers)) {
        /* No watchers left for this path. Clean up. */
        RB_REMOVE(watcher_root, CAST(&loop->inotify_watchers), w);
        uv__inotify_rm_watch(loop->inotify_fd, w->wd);
        uv__free(w);
    }
}

static void uv__inotify_read(uv_loop_t* loop,
    uv__io_t* dummy,
    unsigned int events)
{
    const struct uv__inotify_event* e;
    struct watcher_list* w;
    uv_fs_event_t* h;
    QUEUE queue;
    QUEUE* q;
    const char* path;
    ssize_t size;
    const char* p;
    /* needs to be large enough for sizeof(inotify_event) + strlen(path) */
    char buf[4096];

    while (1) {
        do
            size = read(loop->inotify_fd, buf, sizeof(buf));
        while (size == -1 && errno == EINTR);

        if (size == -1) {
            assert(errno == EAGAIN || errno == EWOULDBLOCK);
            break;
        }

        assert(size > 0); /* pre-2.6.21 thing, size=0 == read buffer too small */

        /* Now we have one or more inotify_event structs. */
        for (p = buf; p < buf + size; p += sizeof(*e) + e->len) {
            e = (const struct uv__inotify_event*)p;

            events = 0;
            if (e->mask & (UV__IN_ATTRIB | UV__IN_MODIFY))
                events |= UV_CHANGE;
            if (e->mask & ~(UV__IN_ATTRIB | UV__IN_MODIFY))
                events |= UV_RENAME;

            w = find_watcher(loop, e->wd);
            if (w == NULL)
                continue; /* Stale event, no watchers left. */

            /* inotify does not return the filename when monitoring a single file
       * for modifications. Repurpose the filename for API compatibility.
       * I'm not convinced this is a good thing, maybe it should go.
       */
            path = e->len ? (const char*)(e + 1) : uv__basename_r(w->path);

            /* We're about to iterate over the queue and call user's callbacks.
       * What can go wrong?
       * A callback could call uv_fs_event_stop()
       * and the queue can change under our feet.
       * So, we use QUEUE_MOVE() trick to safely iterate over the queue.
       * And we don't free the watcher_list until we're done iterating.
       *
       * First,
       * tell uv_fs_event_stop() (that could be called from a user's callback)
       * not to free watcher_list.
       */
            w->iterating = 1;
            QUEUE_MOVE(&w->watchers, &queue);
            while (!QUEUE_EMPTY(&queue)) {
                q = QUEUE_HEAD(&queue);
                h = QUEUE_DATA(q, uv_fs_event_t, watchers);

                QUEUE_REMOVE(q);
                QUEUE_INSERT_TAIL(&w->watchers, q);

                h->cb(h, path, events, 0);
            }
            /* done iterating, time to (maybe) free empty watcher_list */
            w->iterating = 0;
            maybe_free_watcher_list(w, loop);
        }
    }
}

int uv_fs_event_init(uv_loop_t* loop, uv_fs_event_t* handle)
{
    uv__handle_init(loop, (uv_handle_t*)handle, UV_FS_EVENT);
    return 0;
}

int uv_fs_event_start(uv_fs_event_t* handle,
    uv_fs_event_cb cb,
    const char* path,
    unsigned int flags)
{
    struct watcher_list* w;
    int events;
    int err;
    int wd;

    if (uv__is_active(handle))
        return -EINVAL;

    err = init_inotify(handle->loop);
    if (err)
        return err;

    events = UV__IN_ATTRIB
        | UV__IN_CREATE
        | UV__IN_MODIFY
        | UV__IN_DELETE
        | UV__IN_DELETE_SELF
        | UV__IN_MOVE_SELF
        | UV__IN_MOVED_FROM
        | UV__IN_MOVED_TO;

    wd = uv__inotify_add_watch(handle->loop->inotify_fd, path, events);
    if (wd == -1)
        return -errno;

    w = find_watcher(handle->loop, wd);
    if (w)
        goto no_insert;

    w = uv__malloc(sizeof(*w) + strlen(path) + 1);
    if (w == NULL)
        return -ENOMEM;

    w->wd = wd;
    w->path = strcpy((char*)(w + 1), path);
    QUEUE_INIT(&w->watchers);
    w->iterating = 0;
    RB_INSERT(watcher_root, CAST(&handle->loop->inotify_watchers), w);

no_insert:
    uv__handle_start(handle);
    QUEUE_INSERT_TAIL(&w->watchers, &handle->watchers);
    handle->path = w->path;
    handle->cb = cb;
    handle->wd = wd;

    return 0;
}

int uv_fs_event_stop(uv_fs_event_t* handle)
{
    struct watcher_list* w;

    if (!uv__is_active(handle))
        return 0;

    w = find_watcher(handle->loop, handle->wd);
    assert(w != NULL);

    handle->wd = -1;
    handle->path = NULL;
    uv__handle_stop(handle);
    QUEUE_REMOVE(&handle->watchers);

    maybe_free_watcher_list(w, handle->loop);

    return 0;
}

void uv__fs_event_close(uv_fs_event_t* handle)
{
    uv_fs_event_stop(handle);
}
